Filtration cartridges are well known as cleaning media for fluids (liquids or gases) in a wide range of applications. For instance, in the case of gases, filtration cartridges advantageously replace bags made of porous paper or fabric to remove particles therefrom.
In industrial plants, the treatment of process fumes was traditionally done by a dust collector that can contain hundreds or even thousands of bags. These bags must be periodically replaced by new ones as they become saturated or “blinded”, as referred to in the art. Nowadays, bags are progressively replaced by filtration cartridges, in particular cylindrical filtration cartridges provided with a pleated filtration element supported by or between a pair of end members which ensure proper sealing of the cartridges in their receptacles. One important advantage of these cartridges over bags is that the surface area of the filtration element is about 3-4 times that of bags. This allows dust collectors with these filtration cartridges to treat an increased volume of gases. Dust collectors may then be smaller or used for longer periods of time before maintenance or replacement. This last advantage is important in terms of productivity since it decreases the frequency of equipment shutdown for carrying out the maintenance of a dust collector.
The selection or the design of a filtration cartridge must take into account the maximum temperature at which it will operate. Generally, conventional filtration cartridges are only suitable for gases having a relatively low temperature. Cartridges for gases having a relatively high temperature are significantly more costly but are nevertheless limited in terms of the maximum gas temperature that they can handle. Presently, commercially-available filtration cartridges are typically used with gases up to about 200° C. Higher temperatures would result in degradation thereof. This limit is problematic since many industrial plants generate fumes at higher temperatures. Gases must then be cooled before entering the dust collector. Cooling is widely carried out by diluting the hot gases with ambient air. Unfortunately, this increases the volume of gases to be filtered and consequently, it increases the number of required cartridges and thus the size of the dust collector.
The degradation of conventional filtration cartridges generally observed near 200° C. comes for the most part from the materials used for making the end members. These end members are usually made of a polymeric material which could be damaged if heated to more than about 200° C. During manufacturing of such conventional filtration cartridges, one end of the filtration element is immersed into a liquid polymeric material provided in a mold until solidification thereof. Typical polymeric materials used for this purpose are epoxy and polyurethane. At temperatures over about 200° C., the mechanical properties of these polymeric materials decrease to the point that the corresponding parts could easily be broken if subjected to mechanical shocks, such as when cartridges are cleaned by reversed air pulses.
Attempts have been made to avoid the use of polymeric materials in filtration cartridges in order to increase the maximum operating temperature. Ceramic materials have been suggested as an alternative. Unfortunately, it was found that the resistance to mechanical shocks of these ceramic materials was worse than that of their polymeric counterparts.
Metals have much better mechanical properties when compared to polymers or ceramics. However, the main problem is to attach the filtration element to the metal parts. The filtration element is usually a pleated fabric which is typically resistant to a temperature up to about 260° C. This maximum temperature is relatively low compared to the melting point of most metals. For instance, aluminum has a melting point of about 660° C. Immersing a portion of the filtration element directly into molten aluminum would destroy it in a few seconds.